Fluorosilicone polymers are used in a wide variety of applications including precision machine lubricants, working fluids, defoamers, parting agents, fluororubber plasticizers, and liquid fluorosilicone rubber bases.
Recently, liquid fluorosilicone rubber using organosilyl end-capped diorganopolysiloxane was developed. The liquid fluorosilicone rubber has fuel resistance, oil resistance, solvent resistance and chemical resistance equivalent to those of the millable silicone rubber and is applicable to high-precision small-size molding and thin-film coating which are difficult with the millable type. The liquid fluorosilicone rubber is thus expected to find application as parts in transport vehicles (e.g., automobiles and aircraft) and oil-related equipment.
In the prior art, organosiloxy end-capped diorganopolysiloxanes are produced in various ways. US 20080090985 discloses a process including ring-opening polymerization of tris(3,3,3-trifluoropropyl)trimethylcyclo-trisiloxane using triorganosilanol as an end-stopping compound and a siloxane oligomer of an organosodium compound as a polymerization catalyst, and end-capping with hexaorganodisilazane. U.S. Pat. No. 6,492,479 discloses end-capping through reaction of hexaorganodisiloxane in the presence of a linear phosphonitrilic chloride. These processes have the following problems.
(1) Since an organosodium compound is used as the catalyst, condensation reaction of silanol groups at ends of polysiloxane occurs during ring-opening polymerization of tris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane. It is then difficult to control the molecular weight and viscosity.
(2) Since triogranosilanol as the end-stopping compound is unstable and susceptible to dehydration condensation at elevated temperature, it may become hexaorganodisiloxane, reducing the purity of end groups. The water of condensation becomes a new end-stopping compound to complicate the end control.
(3) Since the terminal silanol having a trifluoropropyl group has a low activity, the use of hexaorganodisilazane alone is not regarded to ensure that the product is completely end-capped with organosilyl groups.
(4) When hexaorganodisiloxane is reacted in the presence of a linear phosphonitrilic chloride having high catalytic activity, the terminal silanol is fully capped with an organosilyl group. However, if decomposition residues of linear phosphonitrilic chloride including nitrides and phosphorus compounds are left, they become vulcanization inhibitors when used in liquid silicone rubber. It is difficult to remove in vacuum the decomposition residues of linear phosphonitrilic chloride from high degree-of-polymerization (or high viscosity) oils. Removal requires a special equipment or washing by solvent dilution. Although U.S. Pat. No. 6,232,425 discloses a process for the synthesis of end-stopped diorganosiloxane fluid using tris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane and a hexaorganodisiloxane as the end-stopping compound in the presence of linear phosphonitrilic chloride as the catalyst, this process has the same drawbacks. There exists a need to manufacture high degree-of-polymerization (or high viscosity) organosilyl end-capped fluorosilicone polymers having a controlled viscosity and chain length and featuring a high precision of end-stopping.
Citation List
Patent Document 1: US 20080090985
Patent Document 2: U.S. Pat. No. 6,492,479
Patent Document 3: U.S. Pat. No. 6,232,425